Field of the Invention
The present invention relates to an image processing apparatus, a control method thereof, and a computer-readable storage medium and, more particularly, to a technique of detecting the presence/absence of a movement of an object in a radiation image.
Description of the Related Art
When a radiation image such as an X-ray image is acquired, the image quality of an image may degrade for various reasons. One of the reasons is movement. The movement is a movement of an object during imaging and tends to occur in imaging that puts a burden on a patient such as imaging with a long irradiation time or imaging which requires the patient to hold his/her breath. When a movement occurs, a blur occurs in the acquired image, and the image quality is degraded. A technician who performed the imaging checks whether a movement has occurred by observing the acquired radiation image on a monitor. If a movement has occurred, re-imaging is necessary since the image is not suitable for diagnosis.
However, the monitor used by the technician to check for a movement is often a monitor with low resolution that is just enough to check whether a part necessary for diagnosis has been captured or whether the imaging dose is appropriate. Hence, in order to check for a movement, the entire image needs to be observed by enlarging the image. If such checking occurs each time imaging is performed, not only will it reduce the work efficiency of the technician but it may also cause the technician to miss a movement.
Movement detection by automatically determining whether a movement has occurred in the acquired radiation image is known. As a procedure of detecting movement, Japanese Patent Laid-Open No. 2014-079558 discloses a method of detecting a movement by detecting an edge included in the image and obtaining the high frequency component and low frequency component, based on a feature in which a high frequency component is degraded while a low frequency component is not. On the other hand, Japanese Patent Laid-Open No. 2013-102850 discloses a method of detecting a movement by obtaining a spatial frequency response in the lung fields, based on a feature in which a response in a specific frequency range is attenuated.
However, since the arrangement of Japanese Patent Laid-Open No. 2014-079558 detects the movement by an edge, a movement in which the edge such as a bone does not blur is difficult to detect. For example, since the lung fields move but the ribs barely move, it is difficult to detect a movement that has occurred due to a failure to hold the breath. On the other hand, since the arrangement Japanese Patent Laid-Open No. 2013-102850 detects the movement based on the degradation of a specific frequency range response, it is difficult to distinguish whether the degradation is due to a movement or a structural cause, and the detection accuracy is problematically reduced.